ViewHelper used to override page title

This ViewHelper uses the TYPO3 PageRenderer to set the page title - with everything this implies regarding support for TypoScript settings.

Specifically you should note the setting config.noPageTitle which must be set to either 1 (one) in case no other source defines the page title (it's likely that at least one does), or 2 (two) to indicate that the TS-controlled page title must be disabled. A value of 2 (two) ensures that the title used in this ViewHelper will be used in the rendered page.

If you use the ViewHelper in a plugin it has to be USER not USER_INT, what means it has to be cached!

Why can I not forcibly override the title?

This has been opted out with full intention. The reasoning behind not allowing a Fluid template to forcibly override the page title that may be set through TypoScript is that many other extensions (mainly SEO-focused ones) will be setting and manipulating the page title - and if overridden in a template file using a ViewHelper, it would be almost impossible to detect unless you already know exactly where to look. Enforcing use of the core behavior is the only way to ensure that this ViewHelper can coexist with other extensions in a fully controllable way.